The Demon's Lexicon is a 2009 novel by the Irish author Sarah Rees Brennan.

The story follows two brothers with a sordid past, Nick and Alan Ryves, who fight demons and monsters.

They are on the run from a magician, from whom their mother supposedly stole an amulet, when they meet Mae and Jamie, troubled teenagers who come to them for help.

Throughout the book they face horror, evil and people who just generally want to kill them, while long kept secrets are threatening to unravel.

Very early on, Mae expresses the thought that she may have once had magical powers, but that they went away.